The present invention relates to an automatic means for controlling the dosage of illuminating light projected onto an object to be observed. The brightness is controlled to be suitable for the observation of said object and to prevent the blooming phenomenon.
It is well known to employ a solid state image sensing element incorporated in an endoscope assembly to display the image of an object on a display mans such as a cathode ray tube or the like.
An electronic endoscope assembly incorporating such a solid-state image sensing element is advantageous in that the image can be recorded easily and it will be miniaturized more compactly with progress in the integration technique as compared with conventional systems focussing an optical image through an image-guiding fiber bundle.
When such a solid-state image sensing element is employed and if the incident dosage on the receiver element on the receiving surface is excessively high, an electric charge corresponding to said dosage leaks to the periphery and results in spreading or the blooming phenomenon to make the correct reproduction of an image impossible at these spots and also to make the receiving impossible until the restoration to the normal light conditions.
In order to prevent such blooming phenomenon, it has been proposed to adjust the brightness of the illuminating light mechanically at the light source side. However, when an endoscope assembly is employed in a cavity of a living body, the brightness should be adjusted depending on the distance to an object to be observed, or when the tip of insert member is bent, the distance to the wall of cavity in the living body is varied complicatedly so that it is substantially impossible to adjust the illustrating brightness to a proper level in a short interval.
In addition, when the assembly is employed in the cavity of a living body and when the diseased site is moistened by the body fluid, the reflecting brightness is increased and the proper illustrating brightness depends on the condition of diseased site. On the contrary, when the illustrating brightness is excessively small, the diseased site cannot be photographed distinctly to allow a proper diagnosis.